Stepper Motor Movement without Input (GRBL & UGS)

[kival711]

Hi.
I have created a 3RRR parallel robot, controlled by three NEMA23 stepper motors. I have attached pictures for more context. I am using GRBL and Universal G-Code Sender (UGS) to control the motors. I am certain that all my wiring is coorect since the motors move how I want them to. Whenever I I suply power to the drivers, the stepper motors move a small amount on their own without any G-code input. What could be the issue?

[kolaha]

is GND of PSU connected to GND of Arduino?

[kival711]

No. GND on PSU is connected to GND on each stepper motor driver. Then, negative CP and CW on the drivers are connected to GND on arduino.

[kolaha]

and REST+/- ?

[kival711]

Not connected

[Paul_KD7HB]

@kival711

Whenever I I suply power to the drivers, the stepper motors move a small amount on their own

The stepper motor must move to the nearest full step position when they are powered. That is how stepper motors work!

[kival711]

I see. Is there any way to prevent this from happening?

[Paul_KD7HB]

pour glue into the motor? Ask how you can prevent gravity.

Actually that is why industrial devices use servo motors instead of steppers.

[kival711]

I have used stepper motors in similar applications to this before and have never encountered this issue

[Paul_KD7HB]

Then study the difference in the applications.